SWE202: Interaction Diagrams in Software Construction

Interaction Diagrams

• Interaction diagrams represent interaction (communication, collaboration) between objects/classes and visualize the dynamic aspect of a system.
• UML interaction diagrams consist of sequence diagrams and communication diagrams.

Sequence Diagrams

• Sequence diagrams describe interactions among classes/objects in terms of an exchange of messages over time.
• They are also called event diagrams and are useful for visualizing and validating various runtime scenarios.
• Sequence diagrams capture:
  • Interaction that takes place in a collaboration that either realizes a use case or an operation.
  • High-level interactions between users of the system and the system, between the system and other systems, or between subsystems.

Sequence Diagram Notations

• Actor: represents a type of role played by an entity that interacts with the subject.
• Lifeline: represents an individual participant in the Interaction.
• Activation: a thin rectangle on a lifeline represents the period during which an element is performing an operation.
• Call Message: represents an invocation of operation of target lifeline.
• Return Message: represents the pass of information back to the caller of a corresponded former message.
• Self Message: represents the invocation of message of the same lifeline.
• Recursive Message: represents the invocation of message of the same lifeline, with the target pointing to an activation on top of the activation where the message was invoked from.
• Create Message: represents the instantiation of (target) lifeline.
• Destroy Message: represents the request of destroying the lifecycle of target lifeline.
• Duration Message: shows the distance between two time instants for a message invocation.
• Note: gives the ability to attach various remarks to elements, carrying no semantic force but containing useful information for a modeler.

Collaboration Diagrams

• Collaboration diagrams, also known as communication diagrams, illustrate the relationships and interactions among software objects.
• A collaboration is a collection of named objects and actors with links connecting them, which collaborate in performing some task.
• Collaboration diagrams show:
  • Roles, functionality, and behavior of individual objects.
  • Overall operation of the system in real-time.

Steps for Creating Collaboration Diagrams

• Identify behavior whose realization and implementation is specified.
• Identify structural elements (class roles, objects, subsystems) necessary to carry out the functionality of the collaboration.
• Decide on the context of interaction: system, subsystem, use case, and operation.
• Model structural relationships between elements to produce a diagram showing the context of the interaction.
• Consider alternative scenarios that may be required.
• Draw instance-level collaboration diagrams, if required.
• Optionally draw a specification-level collaboration diagram to summarize alternative scenarios in instance-level sequence diagrams.

Collaboration Diagram Example

• A collaboration diagram illustrates the relationships and interactions among software objects.

Collaboration Diagram Notations

• Objects: shown as rectangles with naming labels inside (object name: class name).
• Actors: instances that invoke the interaction in the diagram, with a name and a role.
• Links: connect objects with actors, depicted as solid lines between two elements.
• Messages between objects: shown as labeled arrows placed near a link, conveying information about the activity and including sequence numbers.